Question

Please answer and explain 3, 4 and 5.

products or a) double deletion b) reciprocal translocation c) pericentric inversion d) paracentric inversion 2. The abbreviated karyotype 2n-1 describes a) nullisomy b) monosomy c) trisomy d) haploid 3. The abbreviated karyotype 2n + 1 + 1 describes: a) Double trisomy b) Tetrasomy c) Double monosomy d) None of these 4. The cultivated bread wheat aestivum although a polyploidy, is fertile because a) has an odd number of chromosome sets b) has an even multiple of chromosome sets c) is a double hybrid d) is propagated by grafting 5. Cultivated bananas and certain seedless fruits are: a) double diploid b) tetraploid c) double haploid d) triploid

Answer 1

2. 2n-1 represents monosomy where there is loss of one of the homologous chromosomes.

3.2n+1+1 represents double trisomy, which means trisomy in two different chromosomes, where there is one extra chromosome due to non-disjunction in 2 different chromosomes. For eg. if there are trisomies at chromosome 14 and 21 then it would be a double trisomy.

Tetrasomy is represented as 2n+2 where there is an extra pair of homologous chromosomes. and double monosomy would be 2n-1-1 due to loss of one homolog in 2 different chromosomes sooption a is correct.

4.Bread wheat is a polyploid but fertile because it has an even multiple of chromosome sets. In case of odd number of chromosome sets , meosis leaves one set of chromosome without a pair which leads to sterility, whereas in case of even chromosome sets all the gametes have n number of chromosomes and none have n+1 hence they are fertile.

5.Cultivated bananas and seedless fruits are triploids.Seeds are formed due to fertilisation of gametes. However in a triploid plant  (3n) gametogenesis after meosis becomes cumbersome as one copy of chromosome cannot pair in the daughter cells therefore fertilisation and seed formation is rare. Triploid plants may be produced by crossing diploid and tetraploid plants.